Overlay-Based Packet Steering

1. A method comprising: receiving, on an overlay-based service path, a service-directed packet at a first network device, wherein the service-directed packet comprises a service header and a service overlay tunnel encapsulation; performing, based on information in the service header, a look-up in a path segment table to locate a next hop adjacency that includes next hop tunnel rewrite information useable to rewrite information in the tunnel encapsulation and identifies a first service node to which the service-directed packet should be forwarded; forwarding the service-directed packet to the first service node on the overlay-based service path; and after the first service node applies a service on the service-directed packet, receiving, on the overlay-based service path, the service-directed packet back from the first service node, wherein the service-directed packet received back from the first service node includes a modified service header.

2. The method of claim 1 , wherein the service-directed packet was intercepted from a network flow intended for a destination device by a service classifier on a second network device and further comprising identifying, based on the look-up in the path segment table using information in the modified service header, the destination device as the next destination for the service directed packet; and forwarding the service-directed packet to the destination device.

3. The method of claim 2 , further comprising: prior to forwarding the service-directed packet to the destination device, de-encapsulating the service-directed packet.

4. The method of claim 1 , wherein the service-directed packet was intercepted by a service classifier on a second network device, and wherein the method further comprises: identifying, based on the look-up in the path segment table using information in the modified service header, the service classifier as the next destination for the service directed packet; and forwarding the service-directed packet back to the service classifier on the overlay-based service path.

5. The method of claim 1 , further comprising: identifying, based on the look-up in the path segment table using information in the modified service header, a second service node as the next destination for the service directed packet; and forwarding the service-directed packet to the second service node on the overlay-based service path.

6. The method of claim 1 , wherein receiving a service-directed packet comprises: receiving a service-directed packet having a layer 2 service overlay tunnel encapsulation.

7. The method of claim 6 , wherein forwarding the service-directed packet to the first service node comprises: forwarding the service-directed packet to the first service node with a layer 2 service overlay tunnel encapsulation.

8. The method of claim 6 , further comprising: encapsulating the service-directed packet with a layer 3 service overlay tunnel encapsulation; and forwarding the service-directed packet having the layer 3 service overlay tunnel encapsulation to the first service node.

9. The method of claim 1 , wherein receiving a service-directed packet comprises: receiving a service-directed packet having a layer 3 service overlay tunnel encapsulation.

10. The method of claim 9 , wherein forwarding the service-directed packet to the first service node comprises: forwarding the service-directed packet to the first service node with a service overlay layer 3 tunnel encapsulation.

11. The method of claim 9 , further comprising: encapsulating the service-directed packet to include a layer 2 service overlay tunnel encapsulation; and forwarding the service-directed packet having the layer 2 service overlay tunnel encapsulation to the first service node.

12. The method of claim 1 , wherein performing the look-up in the path segment table based on the information in the service header of the service-directed packet comprises: using a service path identifier (ID) and a sequence number in the service header to perform the look-up in the path forwarding table.

13. An apparatus comprising: a plurality of network interfaces; a processor coupled to the plurality of network interfaces and configured to: receive, on an overlay-based service path, a service-directed packet that comprises a service header and a service overlay tunnel encapsulation; perform, based on information in the service header, a look-up in a path segment table to locate a next hop adjacency that includes next hop tunnel rewrite information useable to rewrite information in the tunnel encapsulation and identifies a first service node to which the service-directed packet should be forwarded; forward the service-directed packet to the first service node on the overlay-based service path; and receive, on the overlay-based service path, the service-directed packet back from the first service node after the first service node applies a service on the service-directed packet, wherein the service-directed packet received back from the first service node includes a modified service header.

14. The apparatus of claim 13 , wherein the service-directed packet was intercepted from a network flow intended for a destination device by a service classifier on a second network device and wherein the processor is configured to: identify, based on the look-up in the path segment table using information in the modified service header, the destination device as the next destination for the service directed packet; and forward the service-directed packet to the destination device.

15. The apparatus of claim 14 , wherein the processor is configured to de-encapsulate the service-directed packet prior to forwarding the service-directed packet to the destination device.

16. The apparatus of claim 13 , wherein the service-directed packet was intercepted by a service classifier on a second network device, and wherein the processor is configured to: identify, based on the look-up in the path segment table using information in the modified service header, the service classifier as the next destination for the service directed packet; and forward the service-directed packet back to the service classifier on the overlay-based service path.

17. The apparatus of claim 13 , wherein the processor is configured to: identify, based on the look-up in the path segment table using information in the modified service header, a second service node as the next destination for the service directed packet; and forward the service-directed packet to the second service node on the overlay-based service path.

18. The apparatus of claim 13 , wherein the processor is configured to receive a service-directed packet having a layer 2 service overlay tunnel encapsulation.

19. The apparatus of claim 18 , wherein the processor is configured to forward the service-directed packet to the first service node with a layer 2 service overlay tunnel encapsulation.

20. The apparatus of claim 18 , wherein the processor is configured to encapsulate the service-directed packet with a layer 3 service overlay tunnel encapsulation, and forward the service-directed packet having the layer 3 service overlay tunnel encapsulation to the first service node.

21. The apparatus of claim 13 , wherein the processor is configured to receive a service-directed packet having a layer 3 service overlay tunnel encapsulation.

22. The apparatus of claim 21 , wherein the processor is configured to forward the service-directed packet to the first service node with a service overlay layer 3 tunnel encapsulation.

23. The apparatus of claim 21 , wherein the processor is configured to encapsulate the service-directed packet to include a layer 2 service overlay tunnel encapsulation, and forward the service-directed packet having the layer 2 service overlay tunnel encapsulation to the first service node.

24. The apparatus of claim 13 , wherein to perform the look-up in the path segment table based on the information in the service header of the service-directed packet, the processor is configured to: use a service path identifier (ID) and a sequence number in the service header to perform the look-up in the path forwarding table.

25. The apparatus of claim 13 , wherein the processor comprises one or more application-specific integrated circuits.

26. The apparatus of claim 13 , wherein the processor is configured to execute software in memory to performs its operations.

27. One or more non-transitory computer readable storage media encoded with software comprising computer executable instructions and when the software is executed operable to: receive, on an overlay-based service path, a service-directed packet at a first network device, wherein the service-directed packet includes a service header and a service overlay tunnel encapsulation; perform, based on information in the service header, a look-up in a path segment table, to locate a next hop that includes next hop tunnel rewrite information useable to rewrite information in the tunnel encapsulation and identifies a first service node to which the service-directed packet should be forwarded; forward the service-directed packet to the first service node on the overlay-based service path; and receive, on the overlay-based service path, the service-directed packet back from the first service node after the first service node applies a service on the service-directed packet, wherein the service-directed packet received back from the first service node includes a modified service header.

28. The non-transitory computer readable storage media of claim 27 , wherein the service-directed packet was intercepted from a network flow intended for a destination device by a service classifier on a second network device and wherein the computer readable storage media further comprise instructions operable to: identify, based on the look-up in the path segment table using information in the modified service header, the destination device as the next destination for the service directed packet; and forward the service-directed packet to the destination device after receiving the service-directed packet from the first service node.

29. The non-transitory computer readable storage media of claim 27 , wherein the service-directed packet was intercepted by a service classifier on a second network device, and wherein the computer readable storage media further comprise instructions operable to: identify, based on the look-up in the path segment table using information in the modified service header, the service classifier as the next destination for the service directed packet; and forward the service-directed packet back to the service classifier on the overlay-based service path after receiving the service-directed packet from the first service node.

30. The non-transitory computer readable storage media of claim 27 , further comprising instruction operable to: identify, based on the look-up in the path segment table using information in the modified service header, a second service node as the next destination for the service directed packet; and forward the service-directed packet to the second service node on the overlay-based service path.